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| Dissertation / PhD Thesis/Book | FZJ-2013-00465 |
2012
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-89336-788-7
Please use a persistent id in citations: http://hdl.handle.net/2128/4616
Abstract: The manufacture of submicrometer-structured coatings by thermal spraying is currently a subject of increasing research efforts in order to obtain unique and often enhanced properties compared to conventional coatings. Injecting suspensions of submicron ceramic particles into the plasma jet or the flame enables to deposit finely-structured coatings. Such fine microstructures are desired for a large range of applications, such as in the field of thermal barrier coatings (TBCs) for gas turbines. Suspension plasma sprayed (SPS) TBCs show unique mechanical, thermal and optical properties compared to conventional atmospheric plasma sprayed (APS) TBCs. They have thus the potential of providing increased TBC performances under severe thermo-mechanical loading. The benefits of SPS-deposited yttria-stabilized zirconia (YSZ) TBCs are demonstrated, such as very fine porosity, high segmentation crack density and low Young’s modulus. Although segmentation cracks survive during thermal cycling at 1400°C, it was shown that the sintering tendency is high at such temperature exposure. An improvement of the SPS YSZ microstructure was realized by reducing significantly the fraction of unmolten clusters. However, this improvement was not reflected in thermal cycling performances in a burner rig. Further experimental investigations with modified spraying parameters yielded a columnar-structured YSZ coating. This type of microstructure is advantageous for TBC applications since intercolumnar voids can comply with in-plane stresses during thermal cycling, similar to electron beam physical vapor deposited (EB-PVD) TBCs. Further investigations on the SPS process with lanthanum zirconate (La$_{2}$Zr$_{2}$O$_{7}$) as a new promising material for TBCs yielded almost stoichiometric coatings by preventing lanthania evaporation with at the same time columnar-type structure being promising in terms of compliance. The deposition of TiO$_{2}$ coatings by SPS was also investigated. A large range of various microstructures was produced and specific anatase phase content can be tailored. Tree-like columnar structures are particularly attractive for their large surface area that promotes photoactivity. SPS appears as a highly versatile process with great potential for the manufacture of these coatings.
Keyword(s): Dissertation
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